Add support to deploy Dropbox via MDM

Small and large companies use MDM's, like Microsoft Intune, to manage their devices. As Dropbox has a focus on companies, it's one of the only apps that 1: doesn't offer an app to install via MDM for Mac and Windows, 2: doesn't support script for auto account login via MDM. Dropbox does support EMM, but that doesn't to the trick for most companies.

See also https://www.dropboxforum.com/t5/Dropbox-API-Support-Feedback/Revisited-Managed-App-Settings-using-MDM-software-Keys-for-auto/td-p/259006